Atmospheric turbulence is an indicator of mechanical turbulence. Turbulence associated with tiny temperature differences in air, a refractive medium, are detectable by optical and infrared propagation techniques. This implies that these same refractive index variations degrade images made (horizontally or vertically) through a column of air.
Most atmospheric turbulence detectors, including microthermal sensors and a multi-path Differential Image Motion Monitor (DIMM), while very sensitive to turbulent effects between its optical paths, only measure turbulence on a single, or at most, a few, spatial scales. This limitation is critical in studies of the atmosphere, because atmospheric turbulence is expected to deviate from model predictions, especially for horizontal optical paths. While a design can be extended to multiple microthermal sensors to test multiple spatial separations simultaneously, such a design may become impractical with more than a dozen probes per altitude increment.